They’re both weekend-long rock events. Both feature full slates of musical entertainment on two stages.

Besides that, the Union County MusicFest and the Brick City Sound Riot (don’t have much in common. The first will be held outdoors in a suburban park; the other inside a drinking establishment in the middle of the state’s largest city. The two performance areas at the Union County MusicFest will be separated by yards of green grass. The stages at Brick City Sound Riot will be separated by the stairs leading from the ground floor of Kilkenny Ale House to the upstairs room. Union County’s headliners are acts with national profiles and little connection to the current Garden State underground; Brick City is a roll call of North Jersey independent rock. The Union County festival has become an annual tradition; Brick City Sound Riot is an inaugural undertaking.

Yet they can be seen as complementary events. The last headliner at the Union County festival will take the stage at 8:45 p.m. At that time, the Sound Riot will just be gathering steam. And Clark’s bucolic Oak Ridge Park is only a 20-minute drive on the Garden State Parkway from Kilkenny’s in Newark. It’s possible to spend the daylight hours singing along to songs you know well, and then immerse yourself in new sounds after dark.

A relatively modest-sized outdoor event connected to a county fair, the Union County MusicFest has managed to attract some big names to Oak Ridge Park. In recent years, Cheap Trick, They Might Be Giants and Third Eye Blind have taken the stage under the late summer sun. In general, festival organizers have preferred to book crowd-pleasing hitmakers of the ’80s and ’90s, and local legends such as the Smithereens, Southside Johnny and Pete Yorn.

But last year’s event, which drew several thousand spectators to the park, seemed to signal a shift. Train brought a (slightly) more contemporary sound to the event. Co-headliner Spoon, an arty, spare rock act with a radiant critical reputation, had scored its first Top 10 album with “Transference” earlier that year. Cheeky videos made by OK Go, another attraction in 2010, have made the power pop band a very modern thing: a YouTube phenomenon.

The 2011 lineup is a partial turn back to the festival’s prior strategy of relying on vintage hitmakers. Of the three co-headliners, the most recent is Collective Soul, a Florida grunge band whose “Shine” was one of the biggest hits of 1994. Southside Johnny and the Asbury Jukes, who have been entertaining the Garden State for 3½ decades, will be the headliners on Sunday. And the Saturday lineup will be anchored by Blondie, the group that epitomizes late-’70s new wave for millions.

Yet there will also be more young musicians on the festival’s two stages than ever before. The School of Rock — the popular chain of after-school music education centers — will have an enormous presence at this year’s fest. Four School of Rock bands will perform on Friday. Accompanying Alarm singer Mike Peters, a School of Rock All-Star band will open the festivities on Saturday. And on Sunday, that same group of All-Stars will perform a tribute to Bruce Springsteen and the E Street Band.

The Union County MusicFest is free, but traffic in Clark during the event can be daunting, and parking at the festival site is $10. Last year, festival organizers lost track of the money made by parking fees, resulting in an investigation by the county prosecutor’s office that was prompted by the Union County Watchdog Association. The organizers were cleared of any crime, but the investigators discovered that the $1.1 million bill for the event was considerably more than the county government had reported.

The festival is a public event run by the Union County government. Admonished by the prosecutor, the operation is ready to try again.

Below are three acts that should not be missed.

NICOLE ATKINS

When last she played at the Union County Music Festival, singer-songwriter Nicole Atkins was supporting “Neptune City,” her collection of gauzy, cinematic pop songs about dreams, romance and the Jersey Shore, and her band was still called the Sea. But Atkins’ mood has darkened, and her band name has, too — now it’s the Black Sea, and on “Mondo Amore,” it’s pushed into psychedelic territory. “The Tower,” the album’s climax, is six minutes of heavy blues indebted to Janis Joplin and Roy Orbison, and Atkins brings enough lightning and thunder to make the castle walls tremble.

NEON TREES

Despite a name that screams lo-fi, Neon Trees is anything but murky and indirect. The Provo, Utah, quartet plays high-flash synthesizer rock pitched somewhere between the glamorous histrionics of Duran Duran and the slanted, bracing post-punk sound of Franz Ferdinand and Bloc Party. “Animal,” which sports an infectious if slightly nonsensical chorus, hit the Top 10 in 2010 thanks in part to singer Tyler Glenn’s elastic falsetto. He’s got one of the most attention-grabbing hairstyles in modern pop, too — a mohawk that bursts diagonally from his scalp like a black flame. With the exception of the School of Rock acts, Neon Trees is the newest band on the festival bill.

THE SMITHEREENS

At this year’s Maplewoodstock concert, the Smithereens battled sound issues and barking dogs to prove that they are still one of the most formidable live acts in the Garden State. The quartet had attendees dancing on the grass to old favorites such as “Only a Memory” and “House We Used to Live In” — but the material from the recently released “2011” was just as infectious. Remarkably, drummer Dennis Diken may be playing better now than he ever did in the group’s MTV heyday. Frontman Pat DiNizio, by contrast, is the same as he ever was: sardonic, tough, moody and maybe a little professorial, too.